Theretofore, there has been known an infrared-ray reflective substrate configured by disposing an infrared reflective layer on a backing such as glass or film. As the infrared reflective layer, a laminate obtained by alternately laminating a metal layer and a metal oxide layer is widely used. It functions to reflect near-infrared rays such as solar light to thereby impart heat insulating property. As the metal layer, silver or the like is widely used, from a viewpoint of enhancing a selective reflectivity in the infrared region. As the metal oxide layer, indium-tin composite oxide (ITO) or the like is widely used. Generally, in an infrared-ray reflective film using a film backing, with a view to protecting a infrared reflective layer thereof, a protective layer is provided on the infrared reflective layer on a side opposite to the backing.
A key point for reduction in emissivity of the infrared-ray reflective film is to effectively reflect far-infrared rays toward an indoor space by a metal layer comprised in the infrared reflective layer. However, an organic material used as the protective layer for the infrared reflective layer generally contains a C═C bond, a C═O bond, a C═O bond and an aromatic ring, and therefore exhibits large infrared vibrational absorption in a wavelength range of 5 μm to 25 μm within a far-infrared region. Far-infrared rays absorbed by the protective layer are thermally diffused toward an outdoor space by heat conduction, without being reflected by the metal layer. Thus, when an amount of far-infrared rays absorbed by the protective layer becomes larger, the emissivity of the infrared-ray reflective film increases, resulting in failing to obtain a heat insulating effect. As above, in the infrared-ray reflective film, there is a trade-off relationship between emissivity reduction and the durability enhancement.
As means to reduce the emissivity of the infrared-ray reflective film, the following Patent Document 1 proposes a technique of reducing a thickness of the protective layer to reduce an amount of far-infrared rays to be absorbed by the protective layer. However, the reduction in thickness of the protective layer tends to cause deterioration in its protective effect for the infrared reflective layer and thus deterioration in durability of the infrared reflective layer, particularly, the metal layer. Generally, degradation of the metal layer is liable to cause deterioration in heat insulating property due to a rise in far-infrared absorptance, and decrease in visible ray transmittance, in the infrared-ray reflective substrate. In view of this problem, in the Patent Document 1, with respect to a first metal layer such as a silver layer, comprised in an infrared reflective layer, a highly-durable, second metal layer such as a Ni—Cr alloy is additionally disposed in adjacent relation, to thereby impart durability to the first metal layer.